JANUARY 2010

Could your hip bones use a little tofu? Scientists report that moderate intake of soy—at least the amount found in about 1.75 ounces of tofu—was associated with reduced risk of hip fractures among women in the Singapore Chinese Health Study. That’s an amount of soy “higher than the low levels of consumption in the West,” noted lead researcher Woon-Puay Koh, MD, of the National University of Singapore.

The findings represent a bright spot in the mostly disappointing recent research attempting to link soy consumption to better bone health. People in Asia generally have lower rates of osteoporosis than those in the West, and scientists have speculated that high levels of soy foods in Asian diets may be part of the reason. But proof of that notion has been elusive.

In this new study, published in the American Journal of Epidemiology, Dr. Koh and colleagues followed 63,257 Chinese men and women in Singapore, ages 45 to 74 at baseline, for an average 10.6 years. Each participant completed a food-frequency questionnaire to assess his or her dietary intake of soy foods and also answered questions on medical history and lifestyle factors.

During the span of the study, 276 of the men and 692 women suffered a hip fracture. Among women with at least moderate soy intake—2.7 grams or more daily—hip fracture risk was 21% to 36% lower than those consuming the least soy (levels similar to those in the US). A similar association was seen for women consuming at least 49.4 grams of tofu or tofu equivalents and those getting at least 5.8 milligrams per 1,000 daily calories of soy isoflavones.

Researchers suggested that soy isoflavones may help protect the bones of postmenopausal women. These naturally occurring plant hormones, chemically similar to human estrogen, could help replace the bone-protecting estrogen that declines with menopause.

Eating a lot more soy didn’t confer any additional benefits for the women in the study, however. Hipfracture risk levels for all groups were similar except among the one-quarter of women at the bottom of soy intake.

Dr. Koh and colleagues were particularly interested in whether soy intake might also be associated with a reduced risk of hip fractures in men. But here the soy foods struck out: Consumption of soy, tofu and isofla - vones wasn’t linked with any protective benefit among men. (Both genders concerned about bone health, however, can take away lifestyle advice from another finding of the study: Cigarette smoking and higher body mass index—BMI— were both factors in increased risk of hip fractures for men as well as women.)

The findings align with an earlier investigation of soy intake among postmenopausal Chinese women in Shanghai, in which those consuming higher amounts had a 30% reduced risk of hip fracture.

But some experts wonder whether the apparent bone benefits of soy consumption for women can be separated from the overall Asian diet. Combating osteoporosis may not be as simple, they suggest, as adding some tofu to the typical Western fare of burgers and pizza.

For example, a three-year randomized controlled trial by D. Lee Alekel, PhD, at Iowa State Uni versity with 224 postmenopausal women did not demonstrate that 80 or 120 milligrams daily of isoflavones from soy protein exerted a bone-sparing effect (except for a modest protective effect on femoral neck bone-mineral density at 120 mg). Similar research at the University of Miami School of Medi - cine testing 200 milligrams a day versus a placebo on 248 women also failed to find a benefit after two years. Most recently, University of Connec ticut Health Center scientists tested the possibility that soy protein—rather than isoflavones—might benefit women’s bones; after one year comparing four different combinations of soy proteins and/or isoflavones, however, no difference was seen in bone mineral density.

So the jury is still out on soy and bone health. Dr. Koh and colleagues called for further study to confirm their findings and the possible mechanism at work. In the meantime, soy foods can certainly be a part of a healthy diet— particularly soy foods such as tofu and edamame (green soybeans) typical of the Asian diet. Soy-protein bars, soy shakes and other Americanized concoctions may not be made from whole soybeans and can contain added sweeteners, so check the label.

TO LEARN MORE: American Journal of Epidemiology, Oct. 1, 2009; abstract at aje.oxfordjournals.org/cgi/ content/abstract/170/7/901. National Osteoporosis Foundation, 1150 17th Street NW, Suite 850, Washington, DC 20036, (800) 231-4222, www.nof.org